Composites offer high electrical resistance when compared to metallic materials. The latter have been traditionally used in the aeronautical field for manufacturing structures intended to fuel storage, given the mechanical features these materials have with respect to their weight.
The high electrical resistance inherent to composites causes a highly relevant induction effect on the internal systems of the fuel tank. Said effect induces internal electric currents that may generate failures or phenomena which are catastrophic for overall structural integrity.
The phenomena related with moderate or severe electrical discharges occurring in the case of lightning strikes and which must be prevented in a structure manufactured with a material with low electrical conductivity to assure its structural integrity/malfunction of any of the critical electrical equipment/electric arcs inside the tank are:
Hot spots: the high current density in certain specific locations of the structure such as joints or intersection components, can originate high temperature spots. If this temperature exceeds 200° C. (the autoignition point of fuel considered by the FAA/JAA authorities) the fuel may reach its flash point should the suitable stoichiometric concentrations be present inside the tank.
Electric arcs (sparking): the flow of current through materials with different resistivities and in geometrically separated locations can produce voltage drops between amongst one another, releasing discharges in the form of an electric arc and causing the ignition of the fuel/inflammable liquid or vapours contained within the structure.
Electrical equipment malfunction: electrical discharges caused by the lightning strike give rise to high levels of current circulating through the outer structure and may therefore introduce electric current in the internal systems either by shunting or by induction. These effects are capable of causing critical equipment malfunction, generating catastrophic failures.
Patent application PCT/ES05/070133 by the applicant of the present invention describes a method for protecting the set of metal devices arranged inside an electrical discharge-proof fuel tank, manufactured completely or partially with composites, which considers, amongst other items, including insulating inserts in the linear metal devices such that they are subdivided into parts that are insulated from each other.
The present invention refers to an insert of this type that may be used in places with little space available.